Quantum imaging technique takes picture using light that never struck the imaged object

As photographers, we all know that “it’s all about light.” The quality of the light that strikes the scene, gets reflected back into the camera’s lens and carefully focused onto the image sensor.

Well, quantum physics researchers have now developed a fundamentally new quantum imaging technique that uses the property of “entangled” pairs of photons to take pictures. They essentially shine a laser through two non-linear crystals, producing a pair of twin (“entangled”) photons in either crystal: one infrared photon and a “sister” red photon.

If a photon pair is created in the first crystal, only the infrared photon are allowed to illuminate the object. Its sister red photon never encounters the object. And yet, a picture of the object is obtained using the red photons only!

In the experiment, the laser illuminates two separate crystals, creating one pair of twin photons (consisting of one infrared photon and a “sister” red photon) in either crystal. The object is placed in between the two crystals. The arrangement is such that if a photon pair is created in the first crystal, only the infrared photon passes through the imaged object. Its path then goes through the second crystal where it fully combines with any infrared photons that would be created there.

With this crucial step, there is now, in principle, no possibility to find out which crystal actually created the photon pair. Moreover, there is now no information in the infrared photon about the object. However, due to the quantum correlations of the entangled pairs the information about the object is now contained in the red photons – although they never touched the object. Bringing together both paths of the red photons (from the first and the second crystal) creates bright and dark patterns, which form the exact image of the object.

Stunningly, all of the infrared photons (the only light that illuminated the object) are discarded; the picture is obtained by only detecting the red photons that never interacted with the object.